It is well known that halogen-containing polymers are normally susceptible to heat-induced deterioration through autoxidation and that the physical properties of such polymers deteriorate and color changes take place during processing at elevated temperatures. Undesirable color changes often occur within the first 5 to 10 minutes as well as during later stages of the processing. The prime examples of such polymers are the vinyl and vinylidene polymers in which the halogen is attached directly to carbon atoms. Poly(vinyl chloride), copolymers of vinyl chloride and vinyl acetate, and poly(vinylidene chloride), the principal resin in self-clinging transparent food wraps, are the most familiar polymers which require stabilization for their survival during fabrication into pipe, window casings, siding, bottles, wall covering, packaging film, and the like. From a great deal of work in the development of more and more effective heat stabilizers, organotin-based heat stabilizers have become the most efficient and widely used stabilizers for rigid PVC. However, the primary examples of organotin-based heat stabilizers, organotin mercaptides and sulfides thereof, give off an offensive odor even at room temperature and the odor grows worse at the usual processing temperatures.
The offensive odor associated with the use of mercaptans and mercaptides as stabilizers in PVC processing is a long-standing problem. In U.S. Pat. No. 4,062,881, Kugele teaches that sulfides of the organotin mercaptides of mercaptoalkyl carboxylates have reduced odors in comparison with sulfides of the organotin mercaptides of alkyl mercaptocarboxylates, the carboxylic moiety having from 2 to 20 carbon atoms in each case. Dworkin, on the other hand, teaches in U.S. Pat. Nos. 4,104,292; 4,124,618; and 4,187,239 that the organotin mercaptides of mercaptoalkyl octanoate and the sulfides thereof do not exhibit the disagreeable odor which characterizes these classes of organotin compounds.
Now, it has been found, however, that organotin mercaptoalkyl heptanoate and the sulfides thereof not only do not exhibit a disagreeable odor but produce an odor that is actually pleasant—resembling that of pineapples—even when used to stabilize halogen-containing polymers at elevated temperatures. Shorter, less awkward names for the esters and the sulfides—organotin mercaptoalkyl carboxylates and organotin mercaptoalkyl carboxylate sulfides—will be used when appropriate hereinafter.